Hello, If you are completely new to Webflow, things may seem confusing at first. So here's a great resource to get started with webflow basics.
Open the navigator tab using "Z"
Double click on "Values" component
Select any Image on a "value card", and it will get selected and be highlighted in the navigator
On the right side panel click on "Settings" tab to view image settings, and click "Replace Image" button and select the image you want to change it to.